Northern Gulf Coast Digital Elevation Model

Perspective view of DEM

NOAA's National Geophysical Data Center (NGDC) is building high-resolution digital
elevation models (DEMs) for select U.S. coastal regions in the Gulf of Mexico. These
integrated bathymetric-topographic DEMs were developed for NOAA Coastal Survey Development
Laboratory (CSDL) through the American Recovery and Reinvestment Act (ARRA) of 2009
to evaluate the utility of the Vertical Datum Transformation tool (VDatum), developed
jointly by NOAA's Office of Coast Survey (OCS), National Geodetic Survey (NGS), and
Center for Operational Oceanographic Products and Services (CO-OPS). Bathymetric,
topographic, and shoreline data used in DEM compilation are obtained from various
sources, including NGDC, the U.S. Coastal Services Center (CSC), the U.S. Office of
Coast Survey (OCS), the U.S. Army Corps of Engineers (USACE), and other federal, state,
and local government agencies, academic institutions, and private companies. DEMs
are referenced to the vertical tidal datum of North American Vertical Datum of 1988
(MHW), Mean High Water (MHW) or Mean Lower Low Water (MLLW) and horizontal datum of
North American Datum of 1983 (NAD 83). Cell size ranges from 1/3 arc-second (~10 meters)
to 1 arc-second (~30 meters). The NOAA VDatum DEM Project was funded by the American
Recovery and Reinvestment Act (ARRA) of 2009 (http://www.recovery.gov/).

Developed for the Office of Coast Survey (OCS), NOAA Coastal Survey Development Laboratory
(CSDL) in support of NOAA's Vertical Datum Transformation tool (VDatum).

Use Limitations

Not to be used for navigation. Although these data are of high quality and useful
for planning and modeling purposes, they are not suitable for navigation. For navigation,
please refer to the NOS nautical chart series.

Produced by the NOAA National Geophysical Data Center. Not subject to copyright protection
within the United States.

While every effort has been made to ensure that these data are accurate and reliable
within the limits of the current state of the art, NOAA cannot assume liability for
any damages caused by any errors or omissions in the data, nor as a result of the
failure of the data to function on a particular system. NOAA makes no warranty, expressed
or implied, nor does the fact of distribution constitute such a warranty.

All datasets obtained by NGDC were converted to common horizontal and vertical datums
of NAD 83 geographic and MHW, respectively, using Proj4 and VDatum transformation
tool. They were also converted to common file format, ESRI point shapefiles, for visualization
and inspection.

Datasets were visually inspected for identification and editing of data anomalies.
Datasets were then compared with overlapping datasets to ensure data consistency.

Coastline datasets were merged and adjusted to fit satellite imagery.

xyz files of the bathymetric data were surfaced using GMT's 'surface' tool onto a
1 arc-second grid that interpolated to fill empty cells. Points extracted every 10
meters along the coastline were also included to ensure that the bathymetric grid
reached zero at the coast. The resulting Arc ASCII grid was clipped to the coastline
to remove values over land.

xyz files for each input dataset were gridded using MB-System's 'mbgrid' tool, which
utilizes a high-tension spline interpolation method to fill grid cells with no input
elevation values. Preferential weighting was given to more recent, higher-accuracy
datasets. Gridding was performed with a 5% data buffer.

The MHW DEM was quantitatively evaluated by comparing with source datasets and with
elevation values extracted from NGS geodetic monuments. It was visually evaluated
by converting to UTM-zone coordinates (units of meters horizontally and vertically)
and then creating a slope grid to identify gridding artifacts in the DEM.